Network mapping tool for software

Overview:
I am looking for a general overview of what software is available for network mapping capable of monitoring critical applications on the network. My ultimate goal is to determine if a server, a router, etc. goes down, what software is nolonger available.

Statistics:
The network is approximately 6,000 LANs and consists of about 2,000,000 workstations.

Additional Comments:
I am not looking for one specific piece of software. Rather, I am looking for differnet classificationsof network mapping software (focusing on application mapping).

Please e-mail me at PMcCauley@ida.org